Apparatus and process for producing sheets



Aug. 18, 1931. i W. A. DARRAH APPARATUS AND PROCESS FOR PRODUCING SHEETS Filed Aug. l0, 1929 2 Sheets-Sheet l Inventor f @Mw Aug- 18, 93lvv. A. DARRAH 1,819,77l

APPARATUS AND PROCESS FOR PRODUCING SHEETS Filed Aug. 10, 1929 2 Sheets-Sheet 2 f'zyare 3 Patented Aug. 18, 1931 UNITED STATES WILLIAM A. DARRAH, F CHICAGO, ILLINOIS APPARATUS AND PROCESS FOR PRODUCING SHEETS Application led August 10, 1929. Serial No. 384,850.

This invention relates to processes, apparatus and product produced in a novel method of forming a sheet or board. Some of the objects of this invention are to provide eco- I nomical, and effective methods for rapidly p'oducing a strong uniform sheet'or board.

y process also permits of forming boards with considerably greater margins than is ordinarily possible and avoids many limitations present in the usual commercial methods now obtaining.

Some of the objects of this invention are to make possible the formation of a board or sheet from materials which would produce a board or sheet only with great difficulty with the present methods. Another object of this invention is to produce a stronger, tougher board than would be possible from the same materials using present methods. My invention produces a density and interlocking of fibers or particles which is superior to that now obtained. My invention also makes it possible to readily produce a board having a different surface condition from the interior. My process also makes possible the formation of a board containing cementing materials in a manner much superior to present known processes.

The product resulting from the practice of my invention is superior in many ways to present boards. If desired it may be made harder, denser and stronger although my process permits they formation of a light vboard such as is used for insulation. My invention will be described in connection with the formation of board such as is known as wallboard, but it should be understood that by making obvious changes in the process and materials I may produce thinner boards,

sheets, paper or if desired extremely thick and heavy blocks.

My invention. also permits a material shortening of the time of theprocesses and a material shortening of the subsequent drying with a great saving in heat in the drying operation and a material reduction in the cost of drying equipment. Other objects of this invention will be apparent from the specification, claims and drawings attached hereto.

Referring to the drawings:

Figure 1 shows in section partly broken i away a portion of one form of my equipment in slde elevation,

Figure 2 shows a portion o f the same equipment in end elevation also partly broken away.

Figure 3 shows a detail of a portion of the rotating member while Figure 4 shows a vertical elevation partly in section of a portion of the equipment shown in Figure 1 with certain conditions as will be later described.

Figure 5 shows a side elevation partly in section of a roller table, press and dryer which form other steps in my process.

In the drawings 1 represents the housing of a centrifugal rotating member which is carried onshaft 2 which runs in bearings 3 and 4 supported on i destalv. The equipment may be driven rom pulley 6 through a belt or in any conventionall manner. The centrifugal 1 consists of a back or web member 7 supporting a side member I8 enclosed in a housing or shell 9 which is intended pri-` marily to prevent the throwing of moisture or other materials about the room. A perforated member 10 is ruggedly supported in member 8 and l'preferably carries a screen member 11. In order to obtain a greater strength under some conditions I may Vextend shaft 2 as indicated by 12 and apply braces or other reinforcing members as indicated by 13. A drain or outlet 15 is provided in the lower portion of' housing 8 for recovering the white water.

A supporting member 16 which may conveniently take the form of an I-beam or channel member serves to carry movable support 17 which for purposes of illustration isindicated as a trolley consisting of a frame 18' carried on wheels 19 and 20. `The frame 18 supports arms 21 and 22 which carry beam member 23 on which is mounted head box 24. A flexible hose or pipe member 25 delivers stock to head box 24 from any desired source as for example tank 60 the level in which may be varied to adjust the hydrostatic pressure on head box 24 for purposes to be later described, A work table 26 carries a series of r live rolls 27 which may be driven in any desired manner as for example by sprocket 28 by means of/a chain in the usual manner.

It will be evident that movable member 17 and therefore head box 24 may be moved out of position within the cylinder. In Figure 4 the head box is shown in position within the centrifugal 1 whereas `in Figure 1 the head box is shown removed and a second movable member 29 carrying frame 30 on wheels 31 and 32 serves to support frame 33 by means of arms 34 and 35. Frame 33 carries a series of material supports 36, 37 and 38 which for convenience in description are shown as being portions of a substantially cylindrical surface. Work supports 36, 37 and 38 are carried respectively by arms 39, 40 and 4i.

` Head box 24 is provided with a slice 42 provided with adjusting screws 43 designed to control the size of the opening 44 in slice 42. 45 indicates a frame extending from support 33 and carrying doctor 46 which may be of any conventional design as for example a'roller.

Perforated member 10 is formed integrally with the centrifugal device 1. Perforated screen 11 or Fourdrinier wire is held in place by wedge members 47 and 48 provided with a locking member 49 which may take the form of a cylindrical rod or key.

Referring more specifically to Figure 5 the table member 26 carrying live rollers 27 is shown receiving a piece of board or sheet 50 preparatory to passing it through press member 51 which for purposes of illustration is shown formed from rolls 52 and 53, and which serve to press and thereby yhardenthe board. A dryer device 55 is shown in position to re- "ceive the board after leaving press member 51 the board for purposesof illustration being carried on live rolls 56 and leaving dryer 55 on live rolls 57.

One method of operating -the equipment here described and practicing my invention consists in putting centrifugal device 1 into rotation and then sliding carriage 18 along support 16 until head box 24 is in approximately the condition shown in Figure .4. It should be noted that direction of rotation of centrifugal 1 should be approximately the same as the flow of stock from head box 24. Direction of rotation is indicated by the arrow on Figure 3.v Having then adjusted the opening 44 of slice 42 by means of screws 43 to obtain the desired flow of stock valve 58 `is opened, allowing the stock toriow in head box 24. Y

The stock employed may be formed from a great variety .of materials and by many well known methods. One satisfactory form of stock is that now used in the preparation of board or paper depending upon the characteristics of the product which it is desired to produce. In case it is desired to make a board the stock may consist of ground wood to which has been added sizing materials and ifdesired a portion of filler and long fiber. A wide range of materials may be employed in my process and I do not wish to be `re stricted to any special raw material. Such substances as ground wood, ground straw, sugar cane residue, corn stalk fibers or man other materials may be employed. It is pre erable to prepare a portion of the material in such a manner as to produce a considerable percentage of fairly long fibers. Methods of obtaining this result are well known in the art of producing board, paper and similar products and form no part of this invention. It is important to know, however, that owing to the characteristics of the process which I have invented a much wider range of materials may be used than is permissible in present standard practice. As the stock is delivered through opening 44 of head box 24 it falls upon Fourdrinier or screen 11 which may be constructed of wire in the manner similar to present commercial-Fourdriniers or if desired a piece of canvas 0r fabric may be employed.

The centrifugal action due to the rotation of the device subjects the .stock to 'a very powerful force which tends to separate the waterof the stock and leave the solid material on the screen. I prefer to adjust the speed with which the stock leaves opening 44, so that as far as possible the velocity of the stock leaving openin 44 will approximate the linear velocity o screen 11. This arrangement is of some importance in rapidly building a' smooth uniform sheet without ripples or lumps and without creating an unbalance in centrifugal device 1, which in the speeds and sizes employed is quite susceptible to unbalanced conditions. I do not wish to be limited to any particular velocity in device 1 as in general I have found that I can produce a board most rapidly the higher the linear velocity of device 1. On the other hand, if I wish to produce a relatively hard dense board the faster screen 11 travels the more satisfactory the results and the essential limit under the conditions I have described is the strength of the materials and the structure formed therefrom.

If, on the other hand, I wish to form a light somewhat porous board it is desirable to operate at-somewhat lower speeds.

Obviously the most satisfactory speed for any given product will depend upon the nature and conditions of the stock, the rate at whichit is fed from head box 24 and the desired characteristics of the product being produced. As an illustration of operating conditions, I have found that linear velocities in the neighborhood of 3000 to 4000 feet per minute give satisfactory results with certain stock consistencies.

In operating the equipment, I prefer to place a given charge of stock in tank 60 and so adjust the hydrostatic head produced by the liquid in tank 60, that the velocity of the stock leaving opening 44 approximates the linear velocity ofthe member 11. I prefer to-use for tank 60 a1 container which is relatively shallow so that the hydrostatic head will not vary between wide limits-during the emptying of tank 60. Many obvious mechanical expedients may be employed to ac.- complish this result such as raising or lowering the tank 60 to compensate for changes in level of the contents. If desired I may also pump the stock from tank 60 and depend on the pressure delivered by the pump to control the velocity of the stock leaving opening 44. It is to be understood of course that opening 44' extends substantially the entire width of the sheet which is to be formed.

After the desired amount of stock has been applied to Fourdrinier 11 through head box 24 in order to build up the required thickness of sheet, I find it advantageous in many lcases to add a new supply of a different grade .of stock to tank 60. For example in forming a commercial wallboard I prefer to use a rough relatively coarse fiber for theinterior portion of the board and I may add such fillers as are desired to this material. 'Ihe first portion of lstock will tend to segregate, the finer portions going fto the inner surface of theFourdrinier and the coarser fibers build- A ing up to form a felt or mat. The subsequent addition of other portions of stock tends to fill in a portion of the voids between the coarser fibers with the result that kthe product at the end of thi stage usually exhibits a hard'dense surface adjacent to the Walls of the centrifugal or the Fourdrinier and a more porous surface on the inner side.

Inasmuch as it is commercially usually desirable to produce a board or sheet having a high degree of finish on both sides I frequently prefer to add to tank 60-after the board is substantially formed, a new portion of stock which is preferably composed of finer fibers and particles and serves to give a smoothMdense, uniform coating to the surface of the board. For this purpose I may use such materials assulphite or other forms of wood pulp as .prepared for making paper or I may use such materials as gypsum ce- `ment, plasters, etc. depending on the required characteristics. If a paper pulp is employed for this purpose, the resultant product presents a smooth and finished appearance which is very desirable and gives j a surface which is-relatively hard and dense.

One form of sheet which I have found very satisfactory may be made by mixing with the stock a quantity of caustic burned magnesite. The quantity ofthis material may vary within wide limits, but satisfactory results may be obtained when the ratio of 05 magnesite to cellulose fiber inthe finished product is in the neighborhood of one' to six.

The stock is then formed in the way previously described and if desired the finishing coating may have a proportionate-amount of caustic burned magnesite. After as much water as possible Vhas been removed from the material due to the centrifugal action resulting from the rotation of device 1 a limited portion of magnesium chloride may beI applied to the sheet through head box 24 or in any other desired manner the quantity of magnesium chloride being designed to be sufficient to cause a strong set with the caustic The board is then loosened from screen 11 -by inserting a doctor or slice between the `board and the screen. If desired this may be held in position by arm 45 and the centrifugal 1 slowly rotated to loosen the board. Many other methods of accomplishing this result will be apparent to those skilled inthe art.

As the board is loosened it falls by reason of its own weight upon work supports 36, 37 and 38. Frame 29 is then moved along I-beam 16 until the board is over live rolls 27. It is then releasedby rotating work supports 36, 37 and 38 about member 33 thus placing the formed board gently and Without 55. The rolls 52 and 53 may be so` proportioned as'to straighten and flatten the board 50Athus compensating for the curvature resulting from the formation of the board in centrifugal device 1. This operation is preferably carried on while the board is wet and with propercare, as otherwise 4the fibers and structure of the board is likely to be 'damaged. While I do not wish to limit my ini vention to any specific sizes, as these may obviously vary with the requirements in eachparticular case, I have found that when pro' ducing board which in its finished sta-ge may be approximately one-half inch thick it is convenient to use a centrifugal having an internal diameter ranging from twenty to thirty feet. A width of ten feet for the Fourdrinier also gives convenient commercial results. A wide range of dimensions are possible, however, without exceeding the scope of my invention. v t

It will be evident from the description here 105 distortion upon the live rol'ls 27 of table 26.

' given that the process which I have invented makes possible the formation of boards and sheets from a wide range of materials which have hitherto been excluded: An example of this vcondition arises from the fact that in forming'board lor sheets under commercial yconditions the characteristic known as freeness is-of vital importance.- If a given stock is not free enough the time required for forming the sheet will be excessive and the production with a given investment in equip- -ment will'be'materially reduced. This also which is weak andpoor in appearance. Presy ent commercial methods, therefore, it will be noted involve a'balance between the rate of forming the board, the thickness of the board or sheet and the strength of the final product-g Limitations of this class are largely overcome by the device which I have invented, quite -largely for the reason that the powerful forces available make it possible to quickly form a board of almost any desired thicknessindependent of the freeness characteristic. f j

Another advantage obtained from the process 'I- have described `is the much greater amount of water which can be removed from the sheetor board.. In the case of commercial board'practice it is not unusual for the prod- Y uct leaving the Fourdrinier or forming machine to contain'60 to 170% of water and only 30 or 40% of solid material. By means ofthe rocess.. which IA have invented the ratio of olid material to water can be immensely increased so that by proper manipulation if zrdesired, I can produce a sheet or board containing as little as 15 to 25% of water;

This results in large savings of heat and timein the drying operation. The saving in heat results in a reduction in operating cost vwhile the saving in time makes possible the use of shorter and smaller dryers.

The process which I have here disclosed also makes possible the formation ofa board or sheet which is much denser and harder than can be obtained by thevpresent commercial methods. ,This appears to be due partly to thelarge forces -available for removing the water, Vpartlytothe outward pressure of the fibers against the Fourdrinier and partlyto the lling ofthe voids between the fibers. y

It will be noted that none of these factors are available in any where near ythe same degree with present methods.

I am aware that the use of avacuum has been lvadvocatedin connection with the forming of board the vacuum being applied either to the inside ofa c lindrical, moving, per forated drum and t e stock being deliveredf to the outside of the drum. In some cases a vacuum has been applied under a Fourdrinier wire acting to draw out the water. f y

The maximum efect of the vacuum cannot of course exceed atmospheric pressure or in the neighborhood of fourteen pounds per` square inch and most experiments in this line have been conducted with an effective difference of pressure amounting to not 'over six or seven pounds.

l It will be apparent of course that withthe device which I have devised the force available for removing the water and compressinv the board is limited only by the strength o the materials and the structure formed there'- from. If desired, I may utilize forces which are 1000% or more in excess of those available by present methods.

made to accomplish the results which I obytain by means of carrying relatively high pressure on the head box or delivery of the I am aware that many efforts have been stock. i Such efforts have been unsuccessful and apparently are likely to prove unsuccess'- 1 ful for the reason that the desired .result which is formed rather thantoy force itV into v must apparently be obtained by some' force@y which tendstO draw the water from the felt` the felt. The distinction is obvious assome of the effects resulting from the pressure 'system are a destruction of the felt and serious dislocation of the bers from'their natural p Y position, theblocking ofthe felt so that it be-A comes nearly water tight due to the closing of the pores, and the obvious mechanical diiiiculties of controlling the equipment.

It will also be notedthat with present com-v mercial Vmethods the rate of travel of water through thefelt which is formed on the Fourdrinier gradually decreases until it reaches be impractical. l y i the attempt is made to'add a surface coating of some other material,"`y the pores being al' ready filled with ne material,'the rate 4of flow of moisture through the board-'1 already apoint where the flow fwater is so slow as to y If under these conditions l formed will be so slow as to make the process I prohibitive. On the otherhand, by utilizing the centrifugal principle this" difficulty is len- Hl 15 tirely eliminated owin to the much greater l forces' which are availa le.

In describing lmy inventionl Ilhave utilized l 'i I certain speciiic'terms and descriptions for the purpose of clearness. :do not iwish to be' v confined to the exact structure shown or Lde' scribed or the exact method outlined'as many) :departures from my invention will be appar-i ent to those skilled in the` art. Suchy items as dimensions, speeds, pressure', thicknessesy and'w' other characteristics' areyof course, subject to variation with the loperating conditions and the product which itis desired to form.- The mechanical structureshown is intended to be4 diagrammatic and illustrates principles and many obvious equivalents may be employed without departing from the spirit of my invention.

A further feature of my invention consists in the fact that I am able to produce aboard or sheet containing cementing material such as magnesium Oxy-chloride. In order to suocessfully produce a board or sheet containing a material of this nature it is necessary to first remove the major portion of the water and then add a new portion of the cement .forming material such as the magnesium oxysaid stock, third splittingthe cylinder thus formed and removing said cylinder intact to a conveyor, fourth passing said sheet through straightening rolls while wet and finally drying between live rolls.

2. The process of forming sheets which consists in feeding stock at controlled velocitles into a moving centrifugal, removing a portion of the water from said stock. and compressing said fibers while in said centrifugal and finally removing, straightening and drying said sheet.

.3. The process offorming sheets which' consists in feeding stock onto a centrifugal while in motion, removing water from said stock and compressing said fiber while in Said centrifugal, next adding a layerof finer bers to the surface of said sheet and finally removing, straightening and drying said sheet.

In the process of forming sheets by centrlfugal force the step of deliveringA the stock into the centrifugal from a substantially stationary feed nozzle in such a manner that the stock reaches said centrifugal at a substantially constant head and while traveling in the same direction and at substantially the same speed as the centrifugal.

5. In the process of forming sheets by centrifugal force the step of supplying the stock under substantially constant controlled head and in the same direction as the rotation of said centrifugal.

' 6. In the process of forming sheets b centrifugallforce the step which consists 1n delivering stock to sa-id centrifugal in approximately stream line flow with "a minimum of eddies from a stream whose width is substan- 7 The process of forming sheets which consists in feeding stock to a rotating centrifugal, removing a portion of the water from said stock and then supplying a coating of surfacing material, removing a portion of the water from said surfacing material and finally removing ysaid sheet from said centrifugal, straightening and drying.

8. In the process of forming sheets the steps of feeding the fiber to a centrifugal, removing a portion of the water from said fibers and spraying the surface of said partially driedbers with a surfacing-solution thereby strengthening said surface.

9. In the process of forming sheets the steps of feeding the ber toa centrifugal, removing a portion of the water from said fibers and spraying the surface vof said partially dried fibers with a sulphite pulp solution.

10. The process, of forming sheets which consists in feeding a solution of stock containin a cementing material to a moving centrifugal removing a portion of the water from said stock, adding a portion of hardening material to said partially dried sheet, removing said sheet from said centrifugal and straightening while wet and drying.

l1. An apparatus jfor producing sheets comprising a centrifugal device, a feed box arranged to deliver stock to ,the interior of said centrifugal device, and a storage device with means for controlling the pressure of said stock at said feed box, means for compressing the-sheetvwhile in said centrifugal, and means for removing said sheet intact from said centrifugal.

12. In an apparatus for producing sheets a rotary centrifugal device, and a substantially stationary feed box within said centrifugal device arranged to deliver solution to said centrifugal device in the same direction of rotation as said centrifugal device and at substantially the same velocity of the circumference of said centrifugal device, thev nozzle of said feed box extending substantially over the width of said sheet being formed.

13. An apparatus for producing sheets consisting of a centrifugal device, a feedv box adv justable within said centrifugal device,

. means for supplying solution to said feed box under controlled4 pressure conditions, means for removing the formed sheet from said centrifugal device, means for straightening said formed sheet and means for finally drying said formed sheet while straight.

14. In the process of forming sheets by centrifugal force, the step of delivering the stock into the centrifugal from a head box covering substantially the entire Width of the sheet being formed.

15. The process of forming sheets which consists in feeding stock into a centrifugal while in motion, from a substantially stationary feedv box in the form of a stream covering substantially the entire width vof the sheet being produced.

16. The process of forming sheets which consists in' feeding the stock solution to a centrifugal removing a portion of the water from said solution and then adding a second stock solution onto the first and removing a portion of the liquid from above solutions.

17. In the process of forming sheets by centrifugal force, the step of flowing a stock solution'of bers suspended in a liquid into 1 the forming surface of said centrifugal .While said stock is in a stream.

L WILLIAM A. DARRAH. 

